What is the volume of a cylinder with base radius $2$ and height $9$ ? 2 9
Answer: The area of the base is simply the area of a circle: $\pi r^2 = \pi \cdot 2^2 = 4 \pi$ The volume of the cylinder is the area of the base times the height: $B \cdot h = 4\pi \cdot 9 = 36\pi$.